PI-RADS v2.1 Upgrading Rule for Peripheral Zone Lesions Shows Only Fair-to-Moderate Inter-Reader Agreement

PI-RADS v2.1 subcategorization of category-4 peripheral zone lesions (upgraded vs. non-upgraded) had only fair-to-moderate inter-reader agreement (Gwet's AC1 0.29–0.57) across 3 radiologists scoring 375 lesions; csPCa yield for upgraded lesions ranged 39–68% vs. 63–81% for non-u…

• Retrospective single-center lesion-level study; 310 men, 375 MRI-visible peripheral zone lesions, 3 independent readers, MRI-TRUS fusion-targeted biopsy as reference standard; csPCa (ISUP grade group ≥2) present in 47% of lesions.
• Overall PI-RADS categorization achieved moderate-to-substantial agreement, but PI-RADS 4 upgraded/non-upgraded subcategorization dropped to fair-to-moderate (Gwet's AC1 0.29–0.57), undermining its clinical utility as a consistent risk-stratification tool.
• Key limitation: retrospective, single-center design with prelocalized lesions, limiting generalizability to real-world prospective reads where lesion localization itself may add variability.

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